The present invention is generally directed to prosthetic and orthotic devices, and more particularly to an ankle-foot prosthesis for automatic adaptation to level, as well as sloped walking surfaces. Even more particularly, the invention is directed to a device or system for use by lower limb amputees to more easily and safely walk over a variety of sloped terrain, as well as to provide more stability during standing and swaying tasks.
Most currently available prosthetic ankle devices are spring-like structures that operate about one equilibrium point (i.e., one resting angle). These systems can work nicely on level terrain but cause instabilities when lower limb prosthesis users walk on sloped surfaces. Many systems have been described that use hydraulic dampers and/or variations of damping to adjust the properties of the prosthesis (Mauch, 1958—U.S. Pat. No. 2,843,853; Koniuk, 2002—U.S. Pat. No. 6,443,993; Moser et al, 2011—U.S. Pat. No. 7,985,265), including the use of microprocessor-control to adjust damping properties. The inherent problem with damping control of the ankle is the associated loss of energy that occurs. One system exists that uses a motor to change the equilibrium point of a spring-like prosthetic foot (Jonsson et al, 2011—U.S. Pat. No. 8,048,172). However, this system requires multiple steps on a new terrain before it is able to adapt to the new slope. A more desirable system would adapt to different sloped surfaces on each and every step of walking. Lastly, powered ankle-foot systems are being developed (Hugh Herr, Massachusetts Institute of Technology; Thomas Sugar, Arizona State University; Michael Goldfarb, Vanderbilt University). These systems all actively push the prosthesis user with a motor during various times in the gait cycle and require large power sources, e.g., heavy batteries and motors. The only currently available system on the market (iWalk BiOM) is expensive, making it impractical for the majority of lower limb prosthesis users. Also, the high power requirements necessitate carrying additional batteries and frequent charging of batteries.